1. Technical Field of the Invention
The present invention relates to the technical field of bars electrically isolated and in particular the flexible bars used to carry out such connections in electrical systems.
2. Description of the Related Art
Usually, busbars come in the form of a central conductor generally rectangular cross section, which is covered by a sheath or insulation. In the case of flexible bars designed to be easily bent or twisted, they use multiple layers of thin aluminum, copper or other alloys with good electrical properties (conductivity).
In the previous flexible busbars, any of four different methods was used to provide electrical insulation to the flexible busbars. In the first method the electrical insulation of the bars (the multiple thin conductor layers) is accomplished by a sheath coating created by an extrusion process, as illustrated in FIG. 1. FIG. 1 shows a prior art busbar 10 that includes insulation 12, a PVC or halogen-free compound, or an insulating compound such as rubber, that is extruded around the central conductor 14 that usually consists of a staking of strips or laminates 16. The two largest interior surfaces of the insulation 12 are smooth and can be pressed on the center conductor 14 (stack of conductor layers 16). Maximum contact area between the central conductor 14 and the insulation 12 is possible, creating adhesion between two materials 14 and 12, and thus reducing the flexibility of the flexible bar 10. Although during the extrusion process a gap between the central conductor 14 and the insulation 12 exists, the gap will disappear and the flexibility will be reduced when the bar 10 will be bent or twisted.
In a second method, shown in FIGS. 2A and 2B, a prior art busbar 20 has its center conductor 24 insulated with flexible strips of thermoplastic 26, preferably four flexible strips of thermoplastic. The flexible strips 26 have greater dimensions than the outer dimensions corresponding to the central conductor, and are joined together by their longitudinal edges by welding or gluing. The surface of these flexible strips of thermoplastics are smooth or with a small roughness. The smooth interior (or the small roughness) of the sheath also allows maximum contact area between the sheath and the central conductor, creating an adhesion between the two parties when the flexible busbar 20 is bent, fold, or twisted, thus reducing the flexibility of the flexible bar 20. The strips 26 may include a top strip 28 and a bottom strip 30 that overlap edges of side strips 32 and 34, as is shown in FIG. 2A. Alternatively, as shown in FIG. 2B, the strips 26 may include a top strip 38 and a bottom strip 40 that have their edges overlapped by side strips 42 and 44.
Another possibility is to use a heat-shrink sleeve of insulation material, as shown in FIG. 3. The prior art busbar 50 includes a heat-shrink sleeve or sheath 52 of insulation material. The sleeve or sheath 52 has a smooth interior that allows maximum contact area between the sheath 52 and the central conductor 54, creating an adhesion between the sheath 52 and the central conductor 54. Shrink tubing 52 has the disadvantage of applying a pressure against the central conductor 54. This reduces the flexibility of the flexible bar 50.
A fourth possibility is to use a pre-extruded sleeve. The smooth interior of the sheath also allows maximum contact area between the sheath and the central conductor, creating an adhesion between the two sheath and central conductor. A pre-extruded sleeve needs to be significantly larger than the central conductor, to be able to push or pull the sleeve easily relative to the central conductor. The process of placing the sleeve onto the central conductor is mainly a manual process and is expensive.
From the forgoing it will be appreciated that improvements would be desirable with regard to flexible busbars. In particular, it would be desirable to have a busbar with improved flexibility.